The present invention relates to an antenna arrangement comprising a substantially planar patch conductor, feeding means connected to the conductor at a first point and grounding means connected to the conductor at a second point, and to a radio communications apparatus incorporating such an arrangement.
Wireless terminals, such as mobile phone handsets, typically incorporate either an external antenna, such as a normal mode helix or meander line antenna, or an internal antenna, such as a Planar Inverted-F Antenna (PIFA) or similar.
Such antennas are small (relative to a wavelength) and therefore, owing to the fundamental limits of small antennas, narrowband. However, cellular radio communication systems typically have a fractional bandwidth of 10% or more. To achieve such a bandwidth from a PIFA for example requires a considerable volume, there being a direct relationship between the bandwidth of a patch antenna and its volume, but such a volume is not readily available with the current trends towards small handsets. Further, PIFAs become reactive at resonance as the patch height is increased, which is necessary to improve bandwidth.
An object of the present invention is to provide a planar antenna arrangement requiring a substantially smaller volume than known PIFAs and having improved impedance characteristics while providing similar performance.
According to a first aspect of the present invention there is provided an antenna arrangement comprising a substantially planar patch conductor, a feed conductor connected to the patch conductor at a first point and grounding conductor connected between a second point on the patch conductor and a ground plane, wherein the patch conductor incorporates a slot between the first and second points.
The presence of a slot affects the differential mode impedance of the antenna arrangement by increasing the length of the short circuit transmission line formed by the feeding and grounding means, thereby enabling the inductive component of the impedance of the arrangement to be significantly reduced. By a suitable asymmetric arrangement of the slot on the patch conductor, an impedance transformation can be achieved. This would typically be used to increase or decrease the resistive impedance of the arrangement for better matching to a 50 xcexa9 circuit.
An antenna arrangement made in accordance with the present invention can have a substantially reduced separation between patch conductor and ground plane compared with known patch antennas. This enables a significant volume reduction, thereby enabling improved designs of mobile phone handsets and the like.
An antenna arrangement made in accordance with the present invention is also suited for being fed via broadbanding circuitry, for example a shunt LC resonant circuit.
According to a second aspect of the present invention there is provided a radio communications apparatus including an antenna arrangement made in accordance with the present invention.
The present invention is based upon the recognition, not present in the prior art, that the provision of a slot between feed and grounding pins in a PIFA can substantially reduce the inductive impedance of the antenna.
By means of the present invention PIFAs having improved performance and reduced volume are enabled.